In the course of completing an oil and/or gas well, it is common practice to run a string of protective casing into the well bore and then to run the production tubing inside the casing. At the well site, the casing is perforated across one or more production zones to allow production fluids to enter the casing bore. During production of the formation fluid, formation sand is also swept into the flow path. The formation sand is relatively fine sand that erodes production components in the flow path.
In some completions, however, the well bore is uncased, and an open face is established across the oil or gas bearing zone. Such open bore hole (uncased) arrangements are utilized, for example, in water wells, test wells and horizontal well completions. One or more sand screens are installed in the flow path between the production tubing and the open, uncased well bore face.
After the sand screens are in place, water is pumped through the work string for removing drilling debris, filter cake and lost circulation material from the annulus. Large amounts of filter cake and other debris which is not removed from the bore hole can create potential problems with future water and gas coning effects along the horizontal section After the annulus along the uncased well bore has been cleaned, a packer is customarily set above the sand screen to seal off the annulus in the zone where production fluids flow into the production tubing The annulus around the screen may be packed with a relatively coarse sand or gravel which acts as a filter to reduce the amount of fine formation sand reaching the screen.
A common problem experienced during well completion and sand control operations is fluid loss. It is an inherent problem encountered worldwide, due to the high permeability of sandstone reservoirs which allow easy fluid flow into the formation matrix Many wells which are candidates for sand control produce from marginal reservoirs and have insufficient bottomhole pressures to support a column of fluid in the well bore. Still other wells with high pressure zones require high density completion fluids in order to balance the reservoir pressure during the gravel pack operation. In either case, the positive pressure leads to fluid being lost to the reservoir.
This may cause the following problems: (1) the formation may be damaged by swelling of clay minerals within the formation, (2) formation damage caused by particle invasion into the formation, (3) formation damage caused by dissolution of matrix cementation promoting migration of fines within the formation, (4) flow channel blockage by precipitates caused by ionic interactions between well servicing fluids and formation fluids, (5) interactions between well servicing fluids and formation fluids causing emulsion blocks, water block, or changes in wettability of a producing sand, and (6) flow channel blockage due to viscous fluids creating a barrier in the near well bore region. Moreover, some well completion fluids are expensive, presently costing at over $100 per barrel.